The invention relates to apparatus for electrostatic spray painting. In particular, the invention relates to apparatus for electrostatic spray painting having a remote monitoring system for real time display of multisystem process conditions.
Apparatus for electrostatic spray painting employing paint powder is well known and often includes a spray booth having a painting chamber therein. A workpiece conveyor moves workpieces to be painted through the painting chamber while spray guns receive paint powder from hoppers and deliver the paint powder to the painting chamber. A high voltage power supply typically provides a potential of about 100,000 volts between the tip of the spray gun and the workpiece to which the paint powder is to be applied. The workpiece is usually grounded. The electrostatic potential applies an electrical force to the paint particles which leave the jet of the spray gun and carry them into contact with the workpiece. Such spray booth apparatus also includes a roll-away filter assembly of the type disclosed in U.S. Pat. No. 5,107,756 to Diaz which filter apparatus periodically has back pressure applied to canister filters to drive off accumulated paint particles filtered from the booth air to prevent the canister filters from clogging.
Oftentimes such apparatus operate under the control of programmable logic controllers of the type which employ ladder logic or stepwise logic. Unfortunately, such programmable controller versions of spray booth apparatus are relatively inflexible and, in addition, do not provide for the easy of or detection of process conditions.
One such process condition, the humidity of the paint powder, is influenced by the humidity of the high pressure air used to propel the paint powder from the guns. 0It may be appreciated that humidity of the paint powder must be closely monitored to avoid sticking or clogging of the paint powder in the spray gun which could lead to spray gun spitting, yielding and uneven coating on the workpiece or complete clogging of the apparatus altogether.
Other problems typically associated with said spray booth apparatus are the danger of booth fires caused by unwanted arcing between the gun tips and grounded portions of the booth such as the booth walls. Such arcing in a worse case may lead to fire and explosion. Accordingly, in prior spray booth apparatus, ultraviolet arc detectors have been included which might inhibit or cut off the electrical power to the electrostatic supply under certain conditions. Further, apparatus exists or has been taught in the prior art related to systems for detecting fire in a powder spray booth (see U.S. Pat. No. 4,675,203 to Scarbrough).
One problem often encountered in the use of spray booth apparatus is the difficulty for those responsible for maintenance of the system to determine when maintenance may be needed on particular guns of a gun array or on the spray booth as a whole. In particular, the amount of time which the gun is operating determines the amount of wear and tear on the internal components of the gun which, of course, leads to the need for timely preventive maintenance in order to maintain proper uniformity of coatings on the workpieces to be coated.
Although programmable logic controller based systems have in the past provided some remote interrogation capability via modem, it is believed that such systems were relatively inflexible to use because of the use of the ladder logic in the spray booth apparatus.
Accordingly, what is needed is a flexible control system for a spray booth apparatus which allows real time monitoring of a variety of process conditions at a remote location, including arc and fire detection, humidity sensing of the spray powder, gun history and air pressure backwashing of the filtering system.